The term “data processing system” encompasses much more than just computer systems, and may include tablet PCs, hand-held games, PDAs and cellular phones. As a device for inputting user data and commands into a data processing system, touch input devices, or touch screens, are found on a variety of both large and small systems. For example, touch screens are used in a multitude of commercial applications from bank ATMs to video gaming systems, and may be found on the smallest of cellular phones.
Typically, a touch-sensitive surface responds to contact from a stylus or other means of user input, e.g. a finger. The location of the input on the surface corresponds to a particular control function, command or data input for the data processing system. The touch screen may be physically integrated with a visual display device of the system, such as a computer monitor, or it may be a remotely located touch pad.
Several types of touch screen devices are known in the prior art. Resistive or conductive touch screen devices rely on pressure from a user's touch (the user input) to induce electrical contact between two separated conductive grids or surfaces. The electrical contact completes a circuit, altering a uniform flow of current across the grids. The system detects changes in current flow, and uses the sensed information to determine the X and Y coordinate location of the contact on the surface of the touch screen.
Similarly, a capacitive touch screen device conveys a constant and uniform voltage across a capacitive layer or surface. As the input device, which is itself capacitive, touches the surface, the surface deforms and current is drawn to the input device. Consequently, the charge across the capacitive layer decreases. Sensors located along the periphery of the touch screen measure the decrease in charge, and the system uses the various sensor readings to locate the touch input.
Other touch screen devices known in the prior art include: surface acoustic wave (SAW) devices; visual, infrared or RF transmit/receive systems; and electromagnetic digitizers. With SAW devices, the system transmits an acoustic wave across the touch screen surface. Interruptions in the wave, produced by the touch of a stylus or other input device, are detected and used to locate the touch input.
Transmit/receive systems use RF, visual, or infrared energy to locate a stylus in contact with the touch screen. Specifically, energy is either transmitted or received by a stylus and used to calculate the precise position of the contact. Additionally, electromagnetic digitizers use a stylus that generates an electromagnetic field. The magnetic field emanating from the stylus interacts with one or more magnetic fields in the digitizer. The system uses the corresponding changes in the digitizer fields to locate the stylus contact.
Yet another prior art system includes strain gauges mounted in at least three positions around the periphery of the touch screen. Touch inputs generate strain forces, and multiple sensors measure these forces. The system cross-references and correlates the sensor measurements to identify the location of the input.
While each of the systems discussed above have had some success, each also has limitations rendering them difficult or undesirable to use. For example, many of the systems require sophisticated electronics, a very complex wiring scheme or extensive data processing. As a result, these input devices are very expensive to manufacture and integrate into the data processing systems. This is true not only for existing direct contact systems requiring a high resolution grid, but also for RF, visual and IR systems as well.
Further, the use of touch screen keyboards can be cumbersome and slow, as each letter must be “tapped in” one letter at time. More specifically, a traditional touch screen is not capable of recognizing and distinguishing between two or more “touched” locations. Touching one location, maintaining the contact, and touching another location most often produces a line from the first location to the second as the first location is released. Alternatively, the touch screen device may ignore a second touch input, or it may attempt to somehow average multiple inputs into a single input location. In other words, the ability to provide multiple simultaneous points of input is not supported as the touch screen device provides simply one X, Y coordinate pair. In addition, the “tapping action” required makes the touch screen difficult to use if the device is portable (such as a PDA, cell phone, etc.) and/or the subject is holding it while moving or standing.
Additionally, the touch screens affixed to data processing systems are neither transferable between systems, nor are they re-configurable to accommodate various applications. Moreover, a typical touch screen device provides digital signal outputs, simply informing the system that a location of X and Y coordinates is being activated—a binary “on” or “off” reporting of state. The digital signal is then processed by the data processing system in accordance with system design. While this approach may simplify the signal processing requirements of the data processing system, it prevents using the analog signal to detect real-time changes in the input pressure.
Hence, there is a need for a system and method of inputting data into a data processing system that overcomes one or more of the drawbacks identified above.